LED lighting systems are becoming more prevalent as replacements for existing lighting systems. LEDs are an example of solid state lighting and are superior to traditional lighting solutions such as incandescent and fluorescent lighting because they use far less energy, are far more durable, operate longer, can be combined in red-blue-green arrays that can be controlled to deliver virtually any color light, and contain no lead or mercury. As LEDs replace the typical incandescent and fluorescent light fixtures found in many homes and workplaces, the present invention recognizes that it is important to cost effectively dissipate the heat generated by the LEDs used in these systems while maintaining the aesthetically pleasing look of existing lighting hardware.
As illustrated by FIGS. 1A, 1B and 1C, a common prior art LED mounting arrangement results in a substantial portion of the light output going outwardly in the direction of a normal to the top surface of a semiconductor photonic chip 12 as seen in FIG. 1B. As seen in FIG. 1A, a top view of an LED 10, the semiconductor photonic chip 12 is mounted on a substrate 14 which is in turn mounted on a bonding pad 16. The chip 12 is encapsulated beneath an optical lens 18 which focuses the light emitted by the chip 12.
FIG. 1B shows a side view of LED 10 with a plurality of light rays relative to a normal, N, to the top surface of chip 12 illustrating the light emitted by chip 12 as it passes out of lens 18. LED 10 is an XLamp™ from Cree, Incorporated.
FIG. 1C shows an illustrative plot of the light emitted by LED 10 with the y-axis representing the intensity, I, and the x-axis representing the angle, θ, of the emitted light with respect to the normal, N, of FIG. 1B. As illustrated in FIG. 1C, a substantial portion of the light emitted from the LED is along or near the normal, N. Conversely, only a small percentage is emitted transverse to the normal. Angle α, the angle of intensity, is equal to 2*θ.
One common lighting fixture is a ceiling mounted lighting fixture such as a pendant chandelier 200 shown illustratively in FIG. 2A. Fixture 200 may suitably comprise a cord 202 including electrical wires connecting to electrical circuitry located in a ceiling 240, a mounting socket 204, a light bulb 206 which may suitably be an incandescent or fluorescent bulb, and a decorative glass shade 208. Many other variations on ceiling mounted lighting fixtures are common, such as multiple light units with a wide variety of mounts. Similarly, a wide variety of floor and wall mounted lighting fixtures are available. With incandescent bulb and fluorescent bulb versions of pendant chandelier 200, heat from bulb 206 is dissipated into the ambient air around the bulb 206.
FIG. 2B shows one prior art attempt at an LED based chandelier fixture 250. In FIG. 2B, circle 252 represents the diameter of the glass of chandelier fixture 250. In the fixture 250, a first plurality of LEDs 253, 254, 255 and 256 were mounted on a mount 260 having three fins at each corner of the mount 260. A second plurality of LEDs (not shown) was spaced vertically on the mount 260 from the first plurality. All of the LEDs were Nichia LEDs.